Concern over the toxic side effects or lack of specificity of some chemical insecticides has led to the development of biopesticides particularly with insecticidal bacteria and viruses. In general the species Bacillus thuringiensis has been the most successful of all microbial biocontrol agents, and strains of B. thuringiensis are used as a pesticide in the same manner as chemical control agents. Among the naturally occurring Bacillus protein toxins are the polypeptide crystal toxins. These are active against a variety of insects including lepidoptera insects (particularly, B. thuringiensis var. kurstaki and B. thuringiensis var. aizawai); coleoptera insects (particularly, B. thuringiensis var. tenebrionis); and diptera insects (particularly, B. thuringiensis var. israelensis). Additionally, viruses particularly baculoviruses such as Heliothis nuclear polyhedrosis virus (NPV) which are effective against Heliothis spp and Autographa californica nuclear polyhedrosis virus (NPV) which are effective against alfalfa and Trichoplusia ni have been used in biopesticides.
Biopesticides have typically been formulated like chemical pesticides and are usually applied through existing sprayer technology. These formulations may be comprised of the insect pathogen (viruses, such as NPV or bacteria, such as B. thuringiensis), spores and/or crystalline delta endotoxins. However, when used in the field, these formulations have a number of disadvantages. When the biopesticide is exposed to sunlight and ultraviolet radiation the effect can be inactivation of the polypeptides comprising the endotoxin and exposure may damage the nucleic acids of the spores rendering the pesticide less effective. Reference is made to Ignoffo et al. Environ. Entomol., 6:411-415 (1977). This decrease in potency of the formulation necessitates numerous repeated applications to susceptible vegetation of the habitat where insect control is desired. A further disadvantage of these biopesticides and particularly, the Bacillus biopesticides is that in low doses they are feeding inhibitory, but they are not lethal. Insects that ingest a sub-lethal, feeding-inhibitory dose cease feeding for a period of time lasting up to several days. This characteristic, when combined with inactivation of the biopesticide by sunlight while the insects are not feeding can lead to poor control of the target insects.
Attempts have been made to solve the sunlight instability problem by providing biopesticidal formulations wherein insecticidal bacteria and viruses are included in the formulation with a sun screening agent. These formulations independently include both encapsulated and nonencapsulated active toxins, but they all suffer from a number of disadvantages. These disadvantages are specific to each formulation. However, general examples with respect to the encapsulated mixtures include: that the polymers forming the walls of the capsules are not always capable of retaining the sun screening agent within the interior of the capsule, in some instances highly toxic materials are used in the capsule preparation; some of the capsules can only be made by processes that are incapable of yielding particles large enough to provide any substantial barrier of sun screening agent (extremely small particles such as those formed from a two-phase liquid emulsion experience substantially uniform sunlight throughout their interiors); and the capsule coating is susceptible to breakdown in the environment.
Disadvantages with respect to nonencapsulated mixtures include that after application through spray equipment to the crop or target location most of the sun screening agent is not normally dose enough to the organism or toxin to be effective; non-encapsulated mixtures also tend to suffer from the disadvantage described above whereby insects ingest sub-lethal feeding-inhibitory doses but later resume their normal feeding.
The present invention overcomes the disadvantages of the prior art compositions and formulations. Active protein toxins are encapsulated or entrapped in a polymer matrix wherein particles are large enough to comprise a dose that is lethal to the target insect. The process of encapsulation is efficient so that the majority of spores and/or crystals comprising the active toxin or ingredient are encapsulated and a low portion of spores and crystals remain nonencapsulated. The component materials of the composition and process do not inactivate the active ingredient of the biopesticide or leave a residue of toxicological concern. The encapsulated particles are stable both during application to the target site and stable in the environment. The active ingredient is released inside the gut of a susceptible insect when ingested. The composition contains a light-blocking agent which is substantially non-toxic and the agent remains inside the composition matrix during and after application to the target site.